<script type="text/javascript" language="javascript">
    function CreateXMLHttpRequest()
    {
        if ( window.XMLHttpRequest )
        {
            // code for IE7+, Firefox, Chrome, Opera, Safari
            return new XMLHttpRequest();
        }
        else if (window.ActiveXObject )
        {
            // code for IE6, IE5
            return new ActiveXObject("Microsoft.XMLHTTP");
        }
    }
    
    var count = 0;
    
    function ClickCourse(idMenu)
    {
        
        
        var xmlHttp;
        xmlHttp = CreateXMLHttpRequest();
        xmlHttp.onreadystatechange = function()
        {
            count++;
            
            if(xmlHttp.readyState == 4 && xmlHttp.status == 200)
            {
                var kq = xmlHttp.responseText;	
                document.getElementById("main_content").innerHTML = kq;
            }
        }
        
        var serverURL =  'loadCourse?idMenu='+idMenu+'&t=' + (new Date()).getTime();
        
        xmlHttp.open("get", serverURL, true);
		
        xmlHttp.send(null);
    }
</script> 

<div id="lesson_menu">
    <h4>Course</h4>
    <ul>
        <li><a href="#" onclick='ClickCourse(11);'><b>Beginner A1</b></a></li>
        <li><a href="#" onclick='ClickCourse(21);'><b>Beginner A2</b></a></li>
        <li><a href="#" onclick='ClickCourse(31);'><b>Imtermediate B1</b></a></li>
        <li><a href="#" onclick='ClickCourse(41);'><b>Imtermeditate B2</b></a></li>
    </ul>
</div><!-- end lesson_menu -->